Five-Axis Programming

Five-axis machining techniques are rapidly evolving, with many CAD/CAM software developers adding more advanced simulation and collision-avoidance capabilities to five-axis programming packages designed to cut the complex parts used in aerospace, die-mold, and medical machining applications.

CAD/CAM software suppliers are riding the wave of an upturn in the market, as worldwide NC software sales and services grew approximately 6.5% in 2005 to reach a total market of $1.25 billion, according to researcher CIMdata Inc. (Ann Arbor, MI), which also estimates that the market for NC software, including PLM as well as CAM software, will grow 7.2% in 2006 to reach a total of $1.34 billion.

CAM consolidation continued over the past year as the face of the fragmented CAM industry changed with controls and automation giant Siemens' (Munich) bid in January to acquire PLM and CAM software developer UGS Corp. (Plano, TX), which over the past few years has ranked among the largest of CAM developers along with the CATIA development team of Dassault Systèmes (Paris) and IBM Corp. (Armonk, NY).

Amid all the consolidation, CAM software suppliers have looked more toward five-axis and multiaxis machining methods as a way to solidify their offerings for users trying to stay competitive by using more complex manufacturing techniques. Lower prices for five-axis machine tools combined with fierce competition from low-cost Asian and Eastern European manufacturers have played a significant role in garnering keen interest in five-axis and multiaxis machining. New five-axis offerings add the ability to reduce setups on machining complex parts while offering users much more refined collision-avoidance and simulation tools.

Simultaneous five-axis machining allows manufacturers to machine with all five axes of motion at once. Another popular multiaxis machining option is 3+2 machining, where two axes are locked while the others machine parts. "Five-axis machining is an interesting area and an area that we have some specialty," notes Alan Levine, general manager, Open Mind Technologies USA Inc. (Wellesley Hills, MA), a unit of Open Mind Technologies AG (Wessling, Germany), developers of hyperMILL CAD/CAM software.

"We also look at the market and recognize that anybody doing five axis is doing some larger percentage—maybe 70%—of 2-D and 3-D milling, so we're constantly trying to juggle that with our other products," Levine says. "We have some customers with 25 seats that are running 2-D and 3-D, basic stuff, and after evaluation, decided this could be the product."

With its current hyperMILL version 9.5 introduced at IMTS 2006, Open Mind offered users a broad range of machining strategies for 2-D, 3-D, 3+2, and five-axis simultaneous machining, with specialized applications for multiblade, single-blade, and tube milling. The software also added an enhancement of feature technology to help standardize programming of recurring or similar geometries, enabled by more flexible feature definitions. In addition, the package included a new advanced generation of collision-control and avoidance techniques that allow tool positions to be automatically calculated without defining guide curves during five-axis simultaneous machining. In the upcoming hyperMILL version 9.6, which will be out around June, Levine says Open Mind will add multitasking machine support with mill-turn capabilities.

"We've taken our generic set of tools for five-axis machining and broadened them," Levine states. "We've taken that much farther now. We can have a reference curve as a guide, not something you lean into but something that you lean towards, and you can now build in more constraints that consider the actual milling machine, the complexities of the part, so it's that much easier to draw this reference curve.

"We can now do this in what we call an automatic mode; no reference geometry is drawn," Levine adds. "Just by looking at the shapes and having some internal expertise modeled, we can walk around the core-cavity situation, without any reference geometry. We don't want the rotary tables on the milling machine moving to the point of somebody getting seasick. You really want them to move as little as possible. So oftentimes our five-axis solution is a 3+2 or a 4+1 style. We may be tilting the head, and the rotary tables, which are quite fast these days, spin in the middle of a spiral move so you can walk down a complex surface."

Collision-avoidance systems are critical for five-axis users, given the complexity of parts being machined and the difficulty of programming expensive five-axis systems. At EASTEC in May, Delcam will show its updated PowerMILL 7 software. It has improved strategies for a wide array of five-axis machining applications including blades and blisks, aircraft structures, port machining, composite trimming, and engraving of bottle molds.

Among the main advantages of five-axis machining is the ability to save time by machining complex shapes in a single setup. Additional benefits come from the use of shorter cutters that permit faster, more-accurate machining with less vibration, and collision detection, according to Delcam, which has updated its PowerMILL package's collision-avoidance tools that automatically tilt the cutter away from obstacles by a specified clearance. Once clear of the obstacle, the tool returns to the original cutting angle. This is also useful when machining undercut regions, and for optimum control of five-axis machines, PowerMILL allows the tool-axis setting to be adjusted for individual areas of the toolpath; this fine-tuning of toolpaths can make a huge difference in part quality, and allows the machine to run as smoothly as possible.

The system offers full collision control, notes Delcam's Craig Chester. "We can detect any collisions of the toolholders, the machine tool, and the machine tool on the part, to avoid any nasty surprises," he adds. "With a three-axis part, new users know exactly what's going to happen—it's pretty obvious. With a five-axis part, you have no idea what's going to happen on the machine tool," mandating simulation of any potential collisions.

Aerospace machining programs created with Delcam's PowerMILL have been included in a turnkey package developed by Chiron (Charlotte, NC, and Tuttlingen, Germany) for Magellan Aerospace Ltd. (Bristol, UK) to make a range of wing ribs for the Airbus A320 passenger airliner. The package is based around the new Chiron Duo Mill advanced machining system, which incorporates twin 90-kW spindles to allow simultaneous five-axis machining of port and starboard wing ribs. Magellan is one of the largest UK suppliers of detail components into wing build at Airbus, producing about 1300 different parts for Airbus (see our March 2007 cover story on Magellan).

The Duo Mill machine has a 4500-mm overall bed length with twin swivel-head spindles operating on twin working areas. Each working area holds a 2 m — 450-mm rotating cube fixture that can be lifted out for in-cycle loading. It allows full machining of the ribs in two operations—machining one side from billet, and finish-machining the semifinished rib from the previous cycle.

"The reason for having a Duo twin-spindle machine, with two identical setups on either side of the machine, is that we produce a port and a starboard rib at the same time," says Magellan Aerospace's Haydn Martin. "Every time the machine cycles you're getting a finished pair of components, so it's a single-piece flow process that reduces machine downtime." Full five-axis with the swivel heads means there's no need for deburring on features such as rib feet.

In addition to five-axis machining with PowerMILL, Delcam has also added extensive support for continuous five-axis machining to its FeatureCAM 2008 package for the first time. "Many smaller companies can see the benefits of moving to fiveaxis machining, but are intimidated by the complexity of the programming systems that support it," notes Glenn McMinn, Delcam USA president. "With the new release of FeatureCAM, we have made five-axis programming easier, making the technology accessible to a much wider range of companies, especially smaller toolmakers and job shops."

FeatureCAM 2008 offers a variety of methods for controlling the tool axis in five-axis machining for many of the software's finishing strategies. The user can set a specific lead or lean angle—the lead angle is measured in the cutting direction; the lean angle at right angles to the cutting direction. This can be done either to access areas unable to be reached with three-axis machining, or to give better cutting conditions. Alternatively, the tool angle can be set in an orientation either to or from a point, or to or from a line.

Any three-axis toolpath generated in FeatureCAM can be converted to a five-axis toolpath by using automatic collision avoidance to change the tool axis when collisions might occur. The software automatically tilts the cutter away from the obstacle by the specified tolerance, and then returns the cutting angle to the value set for the overall toolpath once the obstacle has been cleared. Various choices are available to control the direction in which the tool is tilted. Other new options include five-axis trimming and swarf machining. These techniques are used for the finishing of composite components and vacuum-formed parts, and for machining pockets in aerospace structures.

More five-axis capability also has been added to GibbsCAM, with the announcement in March by Gibbs and Associates (Moorpark, CA) that its CAM package includes a new option for support of five-axis simultaneous milling. This new option, called GibbsCAM 5-Axis, further extends GibbsCAM's existing machining capability, and provides users with a complete range of five-axis milling functionality.

"In addition to multitask machining, we are seeing an increased use of five-axis machine tools in production manufacturing," notes Bill Gibbs, founder and president of Gibbs and Associates. "Not only do five-axis machine tools minimize the number of setups required to machine a part, but many of the models being created by today's CAD systems contain geometry that can only be machined using five-axis technology. Impellers, turbine blades, porting on cylinder heads, and wing spars are great examples of parts whose geometry requires five-axis."

"Five-axis technology provides the user with the ultimate amount of control when applying tooling to a part," explains Gibbs. "Because of this, collision avoidance, improved surface finish, and reduced tool wear are some of the benefits realized."

New multiaxis functionality and toolpaths for HSM and hard milling were added to CNC Software Inc.'s (Tolland, CT) latest Mastercam X Maintenance Release 2 software. The updated Mastercam software shown at IMTS adds a new engine to the advanced multiaxis toolpaths, which provides a customized interface fine-tuned to specific applications such as impellers and turbine blades.

Depending on the toolpath used, Mastercam's parameter pages display only parameters applicable to the specific toolpath type. Advanced controls for gouge-checking allow full control of the tool motion in Mastercam, and users are not limited to retracting only along the tool axis. Full roughing capability is also available for all the advanced multiaxis machining strategies including plunge roughing.

Tool-axis control and other improvements for five-axis machining will be coming from UGS when the company announces its NX 5 CAM software package this month. "We're adding new functionality for interpolated tool axes, so we get more control over the axis with the tool and its fixture or complex part," says UGS' Vynce Paradise.

With UGS' NX 4 package, users have the capability for curvature matching for five axis, which matches the curvature at the end of the tool by constantly changing the tool axis and allows for fewer passes with larger tools. "If you're using a typical flat-end cutter, it has a radius," notes Paradise. "As you're tipping the radius of the cutter, you can maximize the engagement edge, or the cut surface on the surface you're cutting, so the surface angle of the tool changes. On a complex surface, you do a lot fewer passes than you'd otherwise to do with a smaller cutter, you can use a bigger cutter at various angles and get fewer passes. It's quicker, and it offers a better surface finish."

This article was first published in the April 2007 edition of Manufacturing Engineering magazine.